Compression joint seals
Seal pipe into a hub, bell or socket. No lead, no oakum and no cement. Run PVC into an old cast iron hub without pouring lead.
How it seals
A flexible PVC ring goes into the hub and the pipe goes through it. The donut compresses between the two and seals the joint, with no lead, oakum or mortar.
No lead
No pouring lead, packing oakum or mixing mortar. Seat the donut and the pipe, and the joint is made.
Tie-ins
Tie plastic pipe into an existing cast iron hub or clay bell, or step down a size at the hub.
Ribbed
Multiple ribs help the donut seal against the rough, uneven surfaces of old pipe.
Flexible
Resilient elastomeric PVC flexes with ground movement.
1964
Where Fernco started
Before the first Fernco flexible coupling, there was the donut. Fernco began in 1964 in Ferndale, Michigan, with a donut designed to seal sewer pipe joints. The first Fernco flexible coupling followed in the 1970s. Today, the donut is still made in the USA and still does the same job: a tight seal where pipe meets hub.
Standard sizes
Stocked donuts for the most common jobs, starting with plastic pipe into a service weight cast iron hub. Retail packs, where available, carry a P in front of the part number.
| Part | Cast iron hub | Pipe going in |
|---|---|---|
| 22U-139 | 2″ service weight | 1½″ Schedule 40 plastic or steel |
| 22U-205 | 2″ service weight | 2″ Schedule 40 plastic |
| 33U-205 | 3″ service weight | 2″ Schedule 40 plastic |
| 33U-305 | 3″ service weight | 3″ Schedule 40 plastic |
| 33U-301 | 3″ service weight | 3″ extra heavy cast iron |
| 44U-305 | 4″ service weight | 3″ Schedule 40 plastic |
| 44U-405 | 4″ service weight | 4″ Schedule 40 plastic or steel, or extra heavy soil pipe |
Service weight or extra heavy? The donuts above are made for service weight cast iron hubs. An extra heavy hub is larger inside and may need a different donut. If you have an extra heavy hub, or you’re not sure which you have, reach out before you buy.
Don’t see your size?
Extra heavy hubs, clay bells, sockets and odd sizes. Donuts seal by compression, so the fit is tight and the right part depends on the exact hub and pipe. Send us the details and our team will match it for you.
Donut or coupling?
A donut seals pipe into a hub, bell or socket. If there’s no hub to seal into, you need a coupling.
Use a donut. Clean out the hub and seal the new pipe right into it.
No hub, or a cracked hub cut off? Use a Standard Flexible Coupling on the plain end.
Tying into the outside of a PVC or ABS fitting hub? Use a Socket Coupling.
Installation
Remove old lead, oakum and debris. The hub has to be clean inside.
Coat the outside of the donut with a soap solution.
Push the pipe through the center of the donut about 1½″.
Set the donut and pipe in the hub and drive them in with a hammer and wedge until fully seated.
Test the joint to the engineer’s specs before you backfill or close it up.
These steps follow Fernco’s drive method for hubs with walls 3/8″ or thicker. See the installation sheet for full details.
| Material | Chemical-resistant elastomeric PVC, formulated as a sewer joint material |
| Standards | ASTM D5926 and ASTM C1173 |
| Code | Uniform Plumbing Code (UPC) |
| Joint | Compression seal. No lead, oakum, cement or mortar. |
| Sizes | Hundreds of sizes and configurations. Standard sizes above. |
| Made in | USA |
| Systems | Sewer and DWV |
| Seals into | Hubs, bells and sockets |
| Standard sizes | Service weight cast iron hubs, 2″ to 4″ |
| Other sizes | Extra heavy hubs, clay bells and more. Reach out. |
Installation instructions and the catalog page for Fernco Donuts.
For Schedule 40 plastic into a service weight cast iron hub, pick from the standard sizes. For anything else, measure the inside of the hub or bell and the outside of the pipe, and reach out. Donuts seal by compression, so the fit has to be right.
Extra heavy cast iron is thicker and its hub is larger inside, so a service weight donut may not seal in it. Confirm before you buy. If the pipe is marked, the marking tells you. If not, measure the inside of the hub and reach out.
Yes. The donut seals against the inside of the hub, so the hub has to be clean and free of old lead, oakum and debris.
A soap solution on the outside of the donut.
No. A donut needs a hub, bell or socket to seal into. For a plain or cut end, use a Standard Flexible Coupling.
Yes. Donuts are made for sewer as well as DWV joints. Test the joint before you backfill.
Whether it’s sizing, an odd fitting or a tricky tie-in, our team can help. Reach out, or find your Fernco rep.
